This invention relates to two-part, rapid setting coating systems useful as internal linings for pipelines carrying drinking water.
The use of two-part coating systems, in particular those based on liquid epoxide resins and polyamine curing agents, to form protective linings for drinking water pipelines is well known. Such two-part systems have a demonstrable track record for both the xe2x80x9cin-situxe2x80x9d refurbishment of existing water mains and for the protection of new pipelines. They provide thin, smooth linings with excellent carrying capacity and long term durability. However, these systems exhibit one main limitation for xe2x80x9cin-situxe2x80x9d use in that due to their relatively slow hardening characteristics it is necessary to allow the coatings to harden minimally for 16 hours before returning the pipeline to service.
European Patent Application EP-A-0936235 discloses the use of aliphatic polyisocyanates blended with liquid epoxide resin or non-reactive resin, in combination with selected aromatic diamines, to provide rapid setting coating compositions useful as internal linings for pipelines, in particular as xe2x80x9cin-situxe2x80x9d applied linings for refurbishment of drinking water pipelines. Such compositions, by virtue of their rapid setting characteristics, allow return to service in 2 hours or less with no adverse effects on water quality.
EP-A-0936235 teaches the use of a liquid epoxide resin or non-reactive resin in order to extend the gel time, reduce the heat of reaction and reduce the shrinkage of the pure polyurea systems obtained from the combination of aliphatic polyisocyanate(s) with aromatic polyamine(s).
The present invention provides a two-part coating system that can be applied to internal pipeline surfaces so as to form, at a high cure rate, an impervious lining suitable for contact with drinking water. By virtue of its rapid setting characteristics and insensitivity to moisture, the system of the present invention is particularly useful as an xe2x80x9cin-situxe2x80x9d applied lining for refurbishment of existing drinking water pipelines.
The first part of a two-part coating system according to the present invention comprises one or more aliphatic polyisocyanates, optionally blended with one or more xe2x80x9camine reactivexe2x80x9d resins and/or non-reactive resins.
The aliphatic polyisocyanate(s) employed in the invention can be any organic isocyanate compound containing at least two isocyanate functional groups, said isocyanate groups being aliphatic in nature. Suitable polyisocyanates include hexamethylene-1,6-diisocyanate;2,2,4trimethylhexamethylene diisocyanate; isophorone diisocyanate; 4,4xe2x80x2-dicyclohexylmethane diisocyanate. Alternatively, reaction products or prepolymers derived from the above may be utilized. For the purposes of the present invention, the preferred polyisocyanates are derivatives of hexarnethylene-1,6-diisocyanate. The polyisocyanate compounds have a preferred isocyanate content of between 5 and 50%, with 20-25% being particularly preferred.
The xe2x80x9camine reactivexe2x80x9d resin(s) can be any compound containing functional groups which are capable of reacting with primary or secondary amines. Useful materials include epoxy functional compounds and any compounds containing unsaturated carbon-carbon bonds capable of undergoing xe2x80x9cMichael Additionxe2x80x9d with polyamines, e.g. monomeric or oligomeric polyacrylates. For the purposes of the present invention, liquid epoxide resins or oligomeric polyacrylates are preferred.
Non-reactive resins, whilst not currently preferred in the present invention, may be employed provided that they have no resulting adverse effects on water quality.
The second part of a two-part system according to the present invention comprises one or more polyamines.
Preferably, the second part of the system comprises one or more aromatic polyamines, optionally blended with one or more oligomeric polyamines.
The aromatic polyamine employed can be any organic compound containing at least two primary or secondary amine groups, wherein said amine groups are substituted directly to an aromatic moiety. Suitable aromatic polyamines include diethyl toluenediamine; dimethylthio toluenediamine; 4,4xe2x80x2-methylenebis (2-isopropyl-6-methylaniline); 4,4-methylenebis (2,6-diisopropylaniline); 4,4-methylenebis (2,6-dimethylaniline); 4,4-methylenebis (2,6-diethylaniline); 4,4-methylenebis (2-ethyl-6-methylaniline); 4,4-methylenebis (3-chloro-2,6-diethylaniline). For the purposes of the present invention, diethyl toluenediamine is particularly preferred.
The oligomeric polyamine can be any higher molecular weight organic compound containing at least two primary or secondary amine groups, said amine groups being either aliphatic, cycloaliphatic or aromatic in nature. Suitable compounds include poly (oxypropylene) diamines, poly (oxypropylene) triamines, poly (oxytetramethylene)-di-p-aminobenzoates. For the purposes of the present invention, the preferred compounds are poly (oxypropylene) diamines and poly (oxytetramethylene) di-p-aminobenzoates. The preferred oligomeric polyamines have a molecular weight in the range 400-6000, with molecular weights of 500-3000 particularly preferred. Whilst not currently preferred in the present invention, a second part composed solely of oligomeric polyamines or non-aromatic polyamines may be employed provided that there are no resulting adverse effects on water quality.
Various two-part systems embodying the invention are described below, by way of non-limiting example.